Design and Optimization of a Multi-mode Single-DOF Watt-I Six-Bar Mechanism with One Adjustable Parameter

Abstract

Single degree-of-freedom (DOF) mechanisms have been widely used as motion executers for their compact structure and simple control. However, a single-DOF mechanism can only lead through one specific motion trajectory. Thus, they usually cannot handle multiple tasks well, i.e., realizing a good fit of multiple trajectories. In order to solve such problems, this paper proposes an approach to design multi-mode single-DOF six bar mechanisms, which could individually realize multiple task trajectories using only one driving input via an optimized structure with a selected adjustable parameter (A-Parameter). First, a source mechanism for multi-mode watt-I six bar linkage is designed with 9 candidate adjustable parameters (link lengths, location of pivots, etc.), which enables the same mechanism to fit multiple trajectories by selecting only one parameter to be adjustable. Next, to select the optimal A-Parameter, a multi-objective optimization algorithm NSGA-II + ARSBX is used to demonstrate and analyze the Pareto front optimization under different A-Parameters. Then, we use an example of three different human gait trajectories to show how the synthesis multi-mode single-DOF six bar mechanism is conducted with our approach. In the end, the comparison of task trajectories and the resulting trajectories are presented, which show that the method proposed in this paper is feasible.